Many aircraft are equipped with air-ground data communication equipment for data communication with radios on the ground. These radios on the ground are known as ground stations. Typically, one frequency is used by most of the ground stations in a geographic region such as North America or Europe. The network design requires the avionics to select with which ground station to communicate. The ground station selection logic in the avionics evaluates several parameters including signal strength and location to select which ground station to use.
Usually the ground station selection logic has a fixed signal strength threshold. If the currently selected ground station's signal strength goes below this threshold, the selection logic triggers a handover to another ground station, if one is available. Typically, current ground station selection logic uses only the signal strength of the last message received in determining if the signal strength is below threshold. Field data shows that signal strength can vary considerably, up to 20 dB, from message to message. If the last message had an unusually low signal strength, this can cause the avionics to handoff to a different ground station when it should not. Therefore, using just the last value for signal strength creates additional switching and overhead, thus reducing the efficiency of the network.
Additionally, the signals in such networks are aperiodic, meaning there is not a consistent number of signals received in any given period of time. However, typically there should be a signal every 2 minutes and frequently there are signals more often. The time varying nature of the messages affects attempts to filter or average the data.
Accordingly, there is a need for improved ground station selection logic which overcomes the foregoing deficiencies.